Method of removing patterns from molds



UNITED STATES PATENT OFFICE.

VICTOR LOUGHEED, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR T0 ENTERPRISEFOUNDRY COMPANY, OF SAN FRANCIS'GQ, CALIFORNIA, A CORPORATION OFCALIFORNIA.

METHOD OF REMOVING PATTERNS FROM MOLDS.

No Drawing.

T 0 all to ham it may camera Be it known that I, VICTOR LOUGHEED, acitizen of the United States, residing at San Francisco, in the countyof San Francisco and State of California, have invented a new and usefulMethod of Removing Patterns from Molds; and I do hereby declare that thefollowing is a full, clear, and exact description of my invention, suchas will enable others skilled in the art to which it appertains to makeand use the same.

It has been the practice in making fine and accurate castings, forinstance, dental inlays and the like, to form the mold by setting asuitable mold-forming material as an integral non-parted unit around apattern of wax or similar material, which is easily melted, reduced, ordissipated. But in this practice certain practical difiiculties areencountered, particularly in the problem of removing the material of thepattern completely at a reasonable cost, and without impairment of themold surface. The mold is generally made of some refractory material,usually with plaster-of-Paris (calcium sulfate) as a binder, and thepattern made of wax, molded by any suitable method and has the moldmaterial poured in and set around it.

According to one method, the pattern is removed from the mold bysubjecting the mold to sufficient heat to cause the wax to melt andbecome absorbed by the mold material, subsequent to which the mold issubjected to a temperature sufiiciently higher to cause the absorbed waxto volatilize and burn, until it no longer gives off any gas. It hasbeen definitely determined, in this procedure, that the use of waxeswhich are most completely volatile affords the best results, because anynon-volatile residue burns ultimately to a carbonaceous ash, which isvery objectionable in that it obstructs the pores of the mold materialand thus interferes with venting through the pores of the mold material.

Another practice that has been proposed, and which i the better practicewhen the nature of the mold material will admit, is to immerse theentire mold in hot water, at or near the boiling point, so that as thematerial of the wax pattern reaches its melting point, which is in allcases below the boiling point of water, it is prevented, by theSpecification of Letters Patent.

Patented Jan. 4, 1921.

Application filed August 18, 1919. Serial No. 318,207.

presence of the water, from being absorbed by the mold, and consequentlycan be caused to float out through the opening to the mold cavity. Butthis practice has not heretofore been available with mold materialswhich are in common use, and which best serve the purpose from otherstandpoints, for the reason that at least some of the components of suchmold material are soluble in water to such an extent that in additipn toits desired effect, the water has the undesired effect of dissolvingaway enough of the mold material to impair materially the accuracy ofthe mold cavity, and, consequently, of the ultimate casting.

The object of my invention is to avoid this last-named difliculty, and Iattain this object by rendering the pattern fusing bath inert withrespect to the material of the mold, this being preferably done byusing, instead of pure water, water which, even at the maximumtemperature at which it is employed, already contains in solution suchproportion (preferably up to saturation) of the soluble material ormaterials in the mold as will incapacitate the bath to dissolve anymaterial part of such substances from the mold.

As an example, if a mold material be used which is composed of a finelydivided refractory material with calcium sulfate as a binder, it issimply necessary to supply, to the pattern-melting bath of water, asufficient quantity of ground gypsum to saturate the bath (say bymaintaining an excess or precipitate therein) whereupon the bath may besafely heated even to the boiling point without endangering the moldsurfaces.

By my improved method, the cheaper and more satisfactory mold materialsare made available; the pattern material may be collected on the waterand conserved; accuracy of mold surface is insured; and, as a result, aprocess which has heretofore found its principal uses in the fine artsand the sciences is rendered economically available for commercialproduction of machine parts.

I claim:

1. The improvement in the art of removing from a molded mold thepatterns of fusible material about which the mold is formed, whichconsists in subjecting the mold to a pattern fusing-bath containing asubstance which renders the bath inert with respect to the material ofthe mold.

2. The improvement in the art of Waterfusing the pattern from a moldembodying in its structure a material soluble in water, which consistsin first saturating the water of the bath at the required temperatureWith a supplyof such soluble material, and then subjecting the mold tothe bath.

3; The improvement in the art of removing water fusible patterns frommolds composed of porous material with a Water soluble binder-material,which consists in first supplying to a bath-of water a quantity of 15the binder material at least suflicient to saturate the Water at thepattern-fusing temperature, and then subjecting the mold to such bath.

4. The improvement in the art of casting, which consists in forming apattern from a material fusible in hot water, forming around saidpattern a mold of refractory material having a Water soluble binder,preparing a bath of hot Water saturated with the material of the binder,and subjecting the mold with its contained pattern to the heat of thebath.

Signed at Chicago, Illinois, this 25th day VICTOR LOUGHEED.

. of July, 1919.

